Mitch, I agree with your comment that the vertical stripes look painted on, which is why I think they ARE chemical alteration. What else could produce a feature that is in effect painted on? It is an alteration of the material in the cliff without removing the material, since it preservers the texture of the surrounding cliff face.
If the cliff material was altered without removing it, it mustr be some kind of chemical alteration. The only alternative is an overlay of some other material, maybe sand, whihc is coming down from above, but in that case, why is it sticking to the clif face? It must be chemical alteration of some kind, and that points to fluid flow.
